Non-Faradaic Electrochemical Promotion of Brønsted Acid-Catalyzed Dehydration Reactions over Molybdenum Oxide

Abstract

We report the non-Faradaic electrochemical promotion of a Brønsted acid-catalyzed reaction over a metal oxide surface. Isopropanol dehydration to propylene was used as a probe reaction to study the in situ modification of a molybdenum catalyst film deposited on a yttria-stabilized zirconia solid electrolyte. Upon polarizing the Mo film by +1.5 V, the rate of isopropanol dehydration (1.2 kPa IPA, 3.3 kPa O 2 , 673 K, 135 kPa total pressure) was enhanced by 2.5×. Smaller rate enhancements of c.a. 1.3× were also observed for 2-butanol dehydration to butenes over the same catalyst. Although electrochemical dehydration pathways for this chemistry are implausible, by postulating a hypothetical Faradaic dehydration route, we calculate Faradaic efficiencies greater than 100 for IPA dehydration, confirming the non-Faradaic nature of the promotional effect. This effect is reversible and does not appear to permanently alter the chemistry of the Mo film, based on XPS analysis. We hypothesize that this promotion originates from generation of Brønsted acid sites localized to the three-phase boundary at the catalyst/gas/electrolyte interface and/or acid site strengthening due to electrical polarization. This work demonstrates an alternative handle to promote catalytic turnover, which with further understanding, could be applied toward other Brønsted acid-catalyzed chemistries.

Electrically driven proton transfer promotes Brønsted acid catalysis by orders of magnitude

“…However, attempts to use surface potentials to promote thermochemical catalysis by surface-bound active sites have generally observed weak rate-potential scaling, and the mechanisms underlying these relative-ly modest promotional effects on catalysis remain unclear (Fig. 1B) (13)(14)(15)(16)(17)(18).…”

Electrically-Driven Proton Transfer Promotes Brønsted Acid Catalysis by Orders of Magnitude

“…Consequently, attempts to utilize surface potentials to promote thermochemical transformations generally scale weakly with potential, and the mechanisms underlying these relatively modest promotional effects remain unclear (Fig. 1b) (12)(13)(14)(15)(16)(17).…”

Activation of Lattice Oxygen in Ceria by Plasma Exsolution of MoOx with Atomic Dispersion for NOx Abatement

“…with a balance of acidity and redox performance. , Given the appropriate Brønsted acidity and high thermal stability for molybdenum, cerium–molybdenum mixed oxide has emerged as a promising candidate for the NH 3 -SCR reaction to tackle the challenges of the commercial V 2 O 5 –WO 3 /TiO 2 catalysts. However, due to the facile formation of a solid solution, the poor Mo dispersion on CeO 2 surface limits the adequate exploitation of interfacial lattice oxygen, resulting in the limited activity of NO x reduction at low temperature. − Recently, a specific category of cation precipitation, known as “exsolution”, has emerged as a promising strategy for the fabrication of supported metal oxide catalysts. The exsolved active metal species, distinguished by their high orientation and incorporation into the host oxide structure, exhibit superior catalytic performance and chemical stability. , Therefore, the development of suitable exsolution methods to achieve highly dispersed metal sites on the CeO 2 surface would be beneficial to improve NH 3 -SCR at low temperature.…”